Hydrangeism

Hydrangeism is a term sometimes used informally to describe the phenomenon of hydrangeas changing the color of their flowers. This color change is not a disease or a specific condition but rather a natural process influenced by the soil's pH level. In acidic soils, hydrangeas tend to produce blue flowers, while in alkaline soils, they will typically display pink or red flowers. A neutral pH usually results in purple or a mix of blue and pink. This effect is most pronounced in certain species, particularly Hydrangea macrophylla, commonly known as the bigleaf hydrangea.

The mechanism behind this color shift involves aluminum ions in the soil. In acidic conditions, aluminum is more readily available to the plant, and it is absorbed and transported to the flower petals. The aluminum then binds with pigments called anthocyanins, causing the blue coloration. In alkaline soils, aluminum availability is significantly reduced, preventing the blue color from developing and allowing the pink or red pigments to dominate. Gardeners can intentionally manipulate soil pH to achieve desired flower colors, often using additives like lime to increase alkalinity or sulfur and aluminum sulfate to increase acidity. While not a medical or scientific term in a formal sense, hydrangeism effectively captures this unique and visually striking characteristic of these popular flowering shrubs.